Recently advanced electronics are increasingly required to be more miniaturized or downsized with high performance. Correspondingly, the ball-splines with rotary mechanism used as the component-placement heads in diverse industrial fields including semiconductor fabricating equipment, assembling machines and so are also challenged to help the downsizing of the electronics with high performance.
In Japanese Laid-Open Patent Application No. 2004-128 485, there is described an example of the ball-spline with rotary mechanism, which is used for the component-placement head. With the prior ball-spline with rotary mechanism, a pair of first and second sliders is installed on a spline shaft, spaced away at a preselected interval from each other. The spline shaft is allowed to travel up and down relatively to the sliders by virtue of rolling elements or balls. With the prior ball-spline with rotary mechanism, moreover, there are provided bearing mountings one of which is installed above the first slider and another mounting is below the second slider. Cylindrical members are provided one of which fits over the first slider while another embraces around the second slider. An intermediate cylindrical member is provided which extends across the first and second sliders to fit over both the sliders and connect integrally the sliders with each other. Thus, the cylindrical members are integrally supported by means of the bearings for rotation around the lengthwise center of the spline shaft with respect to a head frame.
With the ball-spline with rotary mechanism built in the component-placement head, the cylindrical members have the beating mountings near the sliders, respectively, which fit snugly into the cylindrical members. The bearings that have fit over bearing mountings are slightly larger in outside diameter than the cylindrical members and therefore the bearings around outer circular surfaces of their outer rings closely fit into the head frame to bear the ball-spline for rotation with respect to the head frame. Thus, the prior ball-spline with rotary mechanism constructed as stated earlier couldn't get out of becoming bigger in the outermost diameter by as twice as the radial thickness of the cylinder member that has fit over the relevant slider. This means the prior art is inevitably disadvantageous to downsizing the ball-spline with rotary mechanism. Moreover, the cylindrical members have to be worked or finely finished over the inside circular surface thereof so as to closely fit over the outside circular surface of the relevant slider. This also means the prior construction as stated earlier involves additional manufacturing steps for ensuring high precision in assemblage.
Referring to FIG. 8, there is shown a conventional ball-spline which is mainly composed of a spline shaft 51 of right circular cylinder having raceway grooves 56 lying diametrically opposed to each other on a circular surface of the cylinder to extend lengthwise of the cylinder, and a slider 52 that fits over or conforms to the spline shaft 51 so as to travel up and down along the spline shaft 51 in a sliding manner by virtue of rolling elements or ball 57. The slider 52 is composed of a carriage 53 of a cylindrical shell that fits over the spline shaft 51, end caps 54 secured on lengthwise opposite ends of the carriage 53, one to each end, end seals 55 arranged on outward ends of the end caps 54 to close an annular clearance between the spline shaft and the slider 52, and a plurality of rolling elements allowed to roll in a recirculating manner through looped circuits. The carriage 53 has raceway grooves 61 cut in an inside circular surface thereof in opposition to the raceway grooves 56 on the spline shaft 51 to define load-carrying raceways 62 between them, and return passages 58 extending in parallel with the load-carrying raceways 62. The end caps have turnaround passages to connect the load-carrying raceways 62 to the return passages 58 to provide the looped circuits made up of the load-carrying raceways 62, return passages 58 and a pair of the turnaround passages. The end caps 54 and end seals 55 are secured on the carriage 53 by means of fastening screws 59. The spline shaft 51 comes into mating with the slider 52 through the rolling elements 57 to provide nearly frictionless linear sliding motion relatively to each other while allowing transmitting torque between them simultaneously. The slider 52 on a circular outside thereof has a key slot 60 into which a key fits to keep the slider 52 against rotation relative to a machine housing the slider 52 therein.
As the advanced electronics become more downsized even with high performance, the ball-spline with rotary mechanism for the component-placement heads in diverse industrial fields including semiconductor fabricating equipment, assembling machines and so on are needed to be downsized with high performance to help the miniaturization or downsizing of the component-placement systems that the ball-spline with rotary mechanism is built in.